Bioethanol is normally produced using yeast (Saccharomyces cerevisiae) to convert glucose into ethanol and carbon dioxide. Conversion of starch- or sugar-based raw materials into ethanol and carbon dioxide is often being referred to as the first generation process. When talking about the second generation process for bioethanol production, lignocellulose is one of a vast variety of possible choices for use as raw material (feed-stock). Lignocellulose consists of cellulose, hemicellulose and lignin and can be converted to glucose and pentoses using acid-, alkali-, and/or enzymatic pretreatment, or a combination of these. S. cerevisiae cannot convert pentoses to ethanol and therefore another kind of microorganism is needed to utilize the hemicellulose part of the raw material.
Some of the obstacles in the establishment of second generation bioethanol productions, are the investment costs and uncertainties in the process. One solution is to integrate the second generation process and the running dry mills of the first generation processes for ethanol production. However, the starch-based processes, which dominate the world market, are dependent on the by-products sold as animal feed, which make the process economically feasible. The quality of the animal feed therefore must not be negatively influenced by the integration. This also puts restraints on the method for utilizing the pentose sugars in the lignocellulosic substrate, as the microorganisms have to be food-grade. The proposed solution is to use food related filamentous Zygomycetes and Ascomycetes fungi, and to produce fungal biomass as a high-grade animal feed from the residues after the distillation (stillage). This also has the potential to improve the first generation process by increasing the amount of the thin stillage directly sent back into the process, and by decreasing the evaporator based problems.
From a human perspective, the world is dependent on fossil fuels for its primary energy supply. In 2010, we consumed 12.7 billion tons of oil equivalents globally, including 32.4% oil, 27.3% coal and peat, and 21.4% natural gas, while biofuels and waste contributed with 10.0%. Amongst the oil consumers, the transport sector completely dominated with 61.5% of the total consumption. Consequently, renewable alternatives for the transportation fuel should be seriously considered, if the fossil fuels are to be replaced.
During the last decade(s), concerns regarding global warming, fossil fuel depletion, and energy security resulted in a wide interest in renewable and environmentally friendly fuels. The dominating biofuel for transportation is ethanol with the annual world production rising from 17.0 to 86.1×106 m3 from 2000 to 2011 (REN21, 2012). It is followed by biodiesel with an annual world production of 21.4×106 m3 in 2011. The largest ethanol producing countries are U.S.A. and Brazil, responsible for the production of 54×106 and 21×106 m3 in 2011, respectively (REN21, 2012). Currently, all industrial scale production of ethanol belongs to the first generation of biofuels. However, the technology to produce second generation ethanol does exist. One of the main obstacles for its implementation is the combination of high risk investments (including technological risks and political/policy risks) with low potential returns.